// Copyright 2016 The Fuchsia Authors
// Copyright (c) 2014 Travis Geiselbrecht
//
// Use of this source code is governed by a MIT-style
// license that can be found in the LICENSE file or at
// https://opensource.org/licenses/MIT

#include <assert.h>
#include <debug.h>
#include <err.h>
#include <iovec.h>
#include <string.h>
#include <sys/types.h>

#define LOCAL_TRACE 0

/*
 *  Calc total size of iovec buffers
 */
ssize_t iovec_size(const iovec_t* iov, uint iov_cnt) {
  if (!iov) {
    return (ssize_t)ZX_ERR_INVALID_ARGS;
  }

  size_t c = 0;
  for (uint i = 0; i < iov_cnt; i++, iov++) {
    c += iov->iov_len;
  }
  return (ssize_t)c;
}

/*
 *  Copy out portion of iovec started from given position
 *  into single buffer
 */
ssize_t iovec_to_membuf(uint8_t* buf, uint buf_len, const iovec_t* iov, uint iov_cnt,
                        uint iov_pos) {
  uint buf_pos = 0;

  if (!buf || !iov) {
    return (ssize_t)ZX_ERR_INVALID_ARGS;
  }

  /* for all iovec */
  for (uint i = 0; i < iov_cnt; i++, iov++) {
    if (iov_pos >= iov->iov_len) {
      iov_pos -= iov->iov_len; /* skip whole chunks */
      continue;
    }

    /* calc number of bytes left in current iov */
    size_t to_copy = (size_t)(iov->iov_len - iov_pos);

    /* limit it to number of bytes left in buffer */
    if (to_copy > buf_len) {
      to_copy = buf_len;
    }

    /* copy data out */
    memcpy(buf + buf_pos, (uint8_t*)iov->iov_base + iov_pos, to_copy);

    /* advance in buffer position */
    buf_pos += to_copy;
    buf_len -= to_copy;

    /* check if we need to copy more data */
    if (buf_len == 0) {
      break;
    }

    iov_pos = 0; /* it is only possible to have fully copied iovec here */
  }

  return (ssize_t)buf_pos;
}
